In general, in a liquid crystal display device that performs color display, one pixel is divided into three subpixels: a red pixel provided with a color filter that allows red light to be transmitted therethrough; a green pixel provided with a color filter that allows green light to be transmitted therethrough; and a blue pixel provided with a color filter that allows blue light to be transmitted therethrough. While color display can be performed using the color filters provided in the three subpixels, about two-thirds of backlight light irradiated onto a liquid crystal panel is absorbed by the color filters. Hence, a liquid crystal display device employing a color filter system, has a problem of low light use efficiency. Hence, attention is focused on a liquid crystal display device employing a field sequential system that performs color display without using color filters.
In a general liquid crystal display device employing the field sequential system, one frame period which is a display period of one screen is divided into three fields. Note that although the field is also called a subframe, in the following description, the uniform term “field” is used. For example, one frame period is divided into a field (red field) in which a red screen is displayed based on a red component of an input image signal; a field (green field) in which a green screen is displayed based on a green component of the input image signal; and a field (blue field) in which a blue screen is displayed based on a blue component of the input image signal. By displaying the primary colors one by one in the above-described manner, a color image is displayed on a liquid crystal panel. Since a color image is displayed in this manner, the liquid crystal display device employing the field sequential system does not require color filters. By this, the liquid crystal display device employing the field sequential system has light use efficiency that is about three times as high as the liquid crystal display device employing the color filter system. Therefore, the liquid crystal display device employing the field sequential system, is suited for increasing luminance and reducing power consumption.
Meanwhile, in a liquid crystal display device, image display is performed by controlling the transmittance of each pixel by a voltage (voltage applied to liquid crystal). In this regard, it takes several milliseconds for the transmittance of a pixel to reach its target transmittance after starting the writing of data (the application of a voltage) into the pixel. Hence, in the liquid crystal display device employing the field sequential system, in each field, a backlight of a corresponding color is switched from, a light-off state to a light-on state after the liquid crystal has responded to a certain extent.
In addition, in the liquid crystal display device, a sufficient image quality may not be obtained, for example, upon displaying a moving image, due to the low response speed of the liquid crystal. In view of this, as measures against the low response speed of the liquid crystal, a drive system called overdrive (overshoot drive) is conventionally adopted. The overdrive is a drive system in which a drive voltage higher than a predetermined gradation voltage corresponding to the data value of the input image signal for the current frame or a drive voltage lower than the predetermined gradation voltage corresponding to the data value of the input image signal for the current frame is supplied to the liquid crystal panel in accordance with a combination of the data value of an input image signal for the previous frame and the data value of an input image signal for the current frame. That is, the overdrive leads to correction of an input image signal that emphasizes a temporal change (but not a spatial change) in data value. By adopting such overdrive, in the current liquid crystal display device employing the color filter system, the liquid crystal responds such that the transmittance almost reaches its target value (target transmittance) in each field.
Note that in relation to an invention of this matter, the following prior art document is known. Japanese Laid-Open Patent Publication No. 2010-250193 discloses an invention of a video display device in which the liquid crystal response time required to obtain a desired gradation value is reduced by changing the display order of colors on a frame-by-frame basis such that a gradation change between fields is reduced.